Dependence of coal liquefaction behaviour on coal characteristics. 6. Product distributions from coals treated in a continuous-flow reactor

Further experimentation with coals in a continuous-flow reactor system at 440 and 455°C confirms the significance of the previous classification of a set of coals by cluster analysis. The greatest yields of distillable products tend to be given by coals of high sulphur content in the middle of the range of the high-volatile bituminous rank classes. Yet the lowest yields of preasphaltene (toluene-insoluble material) tend to be given by coals of high rank and medium sulphur content. The group of low sulphur, low-rank coals (mostly Rocky Mountain province), in a solvent different from that used for the other groups, showed poor conversion and poor distillate yield at the higher temperature. It is concluded that this coal/solvent combination is particularly prone to retrogressive reactions, including coking.     

Dependence of coal liquefaction behaviour on coal characteristics. 8. Aspects of the phenomenology of the liquefaction of some coal

Steps are now being taken to define in more detail the phenomenology of coal liquefaction and to provide a scientific basis for empirical correlations previously established between liquefaction conversion and basic compositional characteristics of coals. The rates of production of oils, asphaltenes and preaphaltenes have been determined at four temperatures for three coals, two of Carboniferous and one of Creaceousage. Products are formed more slowly from the younger coal (which is of slightly lower rank) than from the others, but oxygen, partly as OH but probably mostly in a type of ether, is lost more rapidly. It is estimated that the maximum content of O as cleavable ether is 7.7 atoms/100 C atoms for the younger coal (from Wyoming) and 4.1 and 5.1 for the other two (from Oklahoma and Ohio, respectively). Until ≈ 50% of the amount present in the Oklahoma coal is lost, the rates of removal of oxygen and organic sulphur are approximately equal; beyond this level, the removal of S is more rapid. The loss of organic sulphur from the Ohio coal is slightly faster. Even so, the data do not support the idea that cleavage of thioethers is more rapid than that of ethers and that this is the basic reason why a high organic sulphur content tends to promote liquefaction. Conversion of the pyrite in the Ohio coal to pyrrhotite occurs considerably more rapidly than the pyrite in the Oklahoma coal. In preliminary experiments, it is shown that a curve-resolving programme allows two aromatic and five aliphatic C-H stretching vibrations to be distinguished in FTIR spectra of the hexane-insoluble products, and the distribution changes with degree of conversion. In particular, there is evidence that new aryl methyl are generated during liquefaction, in agreement with evidence from oxidation studies.     

Dependence of coal liquefaction behaviour on coal characteristics. 2. Role of petrographic composition

The techniques used were the same as those used in Part 1 (p 34). Comparison of the liquefaction behaviour of two lithotypes from a Kentucky bituminous coal indicated that in this process pseudovitrinite is a reactive maceral. The hydrogenation of sets of maceral concentrates obtained from a New Mexico sub-bituminous and a Kentucky bituminous coal showed fair correlations between conversion and the total concentration of the presumed reactive macerals (vitrinite, pseudovitrinite and sporinite). Similar concentrates from a Montana lignite showed no such correlation; the one sample that showed a high conversion was a high-density fraction that had a high mineral-matter content and in which nearly all the pyrite in the coal had accumulated. Two samples that have boghead and cannel characteristics gave quite different results on hydrogenation. Both were highly aliphatic in structure and had unusually high hydrogen contents and volatile matter. One, which contained appreciable proportions of sporinite, alginite and resinite, gave essentially no conversion to oil. The other, predominantly vitrinitic but containing alginite as the second most abundant maceral, gave an excellent yield of an oil of low viscosity and aromaticity. It was concluded that although rank, petrographic composition and perhaps geological history are important factors determining liquefaction behaviour, there are other characteristics of coals that may at times override these basic parameters, and the composition of the inorganic matter may be the most significant of these other characteristics.     

Correlation of coal volatile yield with oxygen and aliphatic hydrogen

An interesting correlation has been observed between the volatile yield for three coal conversion processes and the oxygen and aliphatic hydrogen (H_al) content of the coal. The three processes are: (1) rapid pyrolysis in vacuum, (2) hydropyrolysis at ≈10 MPa hydrogen, and (3) liquefaction with tetralin at 400 °C. The volatile yield for the first two processes and for low sulphur coals studied in the third process may be predicted with the equation: Yield≈0.8 O_T+15 H_al where: O_T, the organic oxygen concentration measured by ultimate analysis; and H_al is the aliphatic hydrogen concentration determined from Fourier Transform infrared (FTIR) measurements. The similarity of yields for these processes suggests that they are basically controlled by thermal decomposition. Justification for the above equation is offered by considering a recently developed model for thermal decomposition of coal. The correlation does not fit a group of high sulphur coals studied in the liquefaction programme. These coals have extremely high volatile yields which may be a result of catalytic activity.     

The effect of sulphur present in coal on the course of its reduction in the potassium/liquid ammonia system

Two low-rank coals of high content of sulphur and low sulphur content orthocoking coal were chosen as the subject of study. The process of reduction was carried out twice, for raw and demineralised, by the Radmacher method, coals. Elemental and spectral analyses of the initial coals and the products obtained from them were made. The solubility of the coals in dichloromethane and the average molecular weight of the extracts were determined. The degree of conversion of the coals studied to the products soluble in dichloromethane was found to be surprisingly high regarding the low-rank coals. A hypothesis is put forward that the high content of sulphur in low-rank coals can endow them with certain properties typical of coking coals.     

Dependence of coal liquefaction behaviour on coal characteristics. 1. Vitrinite-rich samples

The liquefaction behaviour of a number of vitrinite-rich coals has been determined in batch autoclaves at temperatures of 385–425 °C and pressures of about 8.6 MPa (85 atm) of hydrogen. In one set of experiments, impregnated ammonium molybdate was used as catalyst, with no added liquid as vehicle. In a second set, a proprietary catalyst was used and anthracene oil served as vehicle. Lignites, sub-bituminous, medium-volatile and low-volatile bituminous coals gave relatively poor conversions. However, a lignite sample that had been subjected to ion-exchange treatments gave high conversion, and the viscosity and structural parameters of the products varied with the nature of the treatment. In general the highest conversions were observed for coals in the high-volatile bituminous range, but within this broad range and for the comparatively small set of samples studied neither these data nor the structural characteristics of the products show any very evident correlation with rank parameters or with the geological history of the sample. Two geologically young bituminous coals from the Pacific Coal Province gave excellent conversions; both had very high mineral-matter contents, a fact that may be very relevant.     

Distribution of sulphur in one-dimensional pulverized-coal flames

Results of experiments to determine the distribution of fuel sulphur in one-dimensional pulverized-coal flames are presented for two high volatile A bituminous coals, one pulverized into three size fractions, and one subbituminous A coal. A complete determination of the sulphur fed into the flame was obtained through measurement of SO₂, H₂S, COS, CS₂, and solids sulphur. SO₂ is the predominant gas-phase species followed by H₂S with COS and CS₂ being present in smaller amounts. Sulphur is released from smaller particles more rapidly than from larger ones. Sulphur release parallels, to some extent, nitrogen release except at the longer residence times for the subbituminous coal and one of the bituminous coals. A substantial fraction of the sulphur contained in these coals is inorganic. First-order rate constants for sulphur release from the solid are presented. The effects of internal mass transfer on the kinetics are presented for one of the bituminous coals by considering the sulphur release process to consist of a first-order devolatilization reaction occurring in parallel with diffusion of the sulphur to the particle surface and first-order deposition back to the solid matrix. Particle size effects are accounted for in the model, and the data on solids sulphur are used to obtain activation temperatures for the devolatilization reaction and the deposition reaction of 29 900 and 31 400 K, respectively.     

Ignition characteristics of coal blends in an entrained flow furnace

Ignition tests were carried out on blends of three coals of different rank - subbituminous, high volatile and low volatile bituminous - in two entrained flow reactors. The ignition temperatures were determined from the gas evolution profiles (CO, CO₂, NO, O₂), while the mechanism of ignition was elucidated from these profiles and corroborated by high-speed video recording. Under the experimental conditions of high carbon loading, clear interactive effects were observed for all the blends. Ignition of the lower rank coals (subbituminous, high volatile bituminous) enhanced the ignition of the higher rank coal (low volatile bituminous) in the blends. The ignition temperatures of the blends of the low rank coals (subbituminous-high volatile bituminous) were additive. However, for the rest of the blends the ignition temperatures were always closer to the lower rank coal in the blend.     

Effect of Wyodak coal properties on hydroliquefaction reactivity

The effect of Wyodak coal properties on liquefaction reactivity as measured by distillate yield and cyclohexane conversion has been investigated. Spot samples of four Wyodak subbituminous coals from the Anderson and Canyon coal seams in the Powder River Basin of NE Wyoming were liquefied in microautoclave and batch reactor experiments. Runs were made using two different Wyodak coal-derived solvents. Emphasis in this work was directed toward correlation of C₄-700 K distillate yield and cyclohexane conversion as functions of measurable physical, chemical and petrographic properties of the feed coal. Reactivity rankings were found to be the same using either measure of coal reactivity. However, the data indicated that distillate yields were a function of both solvent quality and feed coal properties. For each solvent studied, selected coal properties, including carbon content, total and organic sulphur content, vitrinite content and total reactive maceral (vitrinite plus exinite) content, were found to give statistically significant correlations with distillate production and cyclohexane conversion. Pyritic and sulphate sulphur contents did not appear to enhance liquefaction yield or conversion at the reaction conditions studied. However, any catalytic effects due to pyrite or sulphate sulphur may have been masked by the use of two high quality liquefaction solvents.     

Dependence of coal liquefaction behaviour on coal characteristics. 3. Statistical correlations of conversion in coal-tetralin interactions

The liquefaction behaviour of coals can vary over a wide range depending on both their chemical and petrographic characteristics. Sixty-eight coals have been studied under standard liquefaction conditions, in the presence of tetralin but with no added catalyst or molecular hydrogen. Simple correlations between conversion and individual coal parameters proved unsatisfactory. A novel approach utilizing a stepwise multiple regression analysis led to a number of linear equations relating conversion simultaneously to several coal characteristics. Such linear equations provide a basis for accurately predicting liquefaction behaviour and confirm that wise selection of appropriate feedstocks will have an important economic value. It seems permissible to infer that the behaviour of coals in any processing conditions can only be adequately accounted for by consideration of at least three coal properties; attempts to correlate coal properties solely with a rank parameter, such as carbon content, can no longer be considered adequate.     

Chemical reduction of sulphur dioxide to free sulphur with lignite and coal. 1. Steady-state reaction chemistry and interaction of volatile components

The chemical reduction of SO₂ with North Dakota lignite has been discovered to be a facile reaction which occurs at a relatively low temperature of 600–650 °C. Under optimum conditions, the reaction chemistry can be controlled to allow 85–90% conversion of SO₂ to free sulphur in a single-stage reaction. Major by-products of the reaction are CO₂, H₂O and a free-flowing ash. The high sulphur yield from this reaction exceeds the calculated thermodynamic gas phase equilibrium value of 66–70%. The higher experimental yield was found to be due in part to a catalysed re-equilibration of the gaseous products in the exit line. With lignite and low-rank coals, the mechanism of SO₂ reduction appears to involve reaction of hydrocarbons within the pores structure and thus allows complete conversion of the volatile matter with no tar formation. Volatilization and tar formation successfully compete with SO₂ reduction in bituminous coals under the same reaction conditions.     

Distribution of sulphur in coal seams with special reference to the Tertiary coals of North-Eastern India

This investigation makes a systematic study of the distribution of the forms of sulphur in the Tertiary coals of North-Eastern India, i.e. coals of Upper Assam and Arunachal Pradesh, to delineate the areas of low sulphur content and high sulphur content with a low proportion of organic sulphur. These coals have, in general, a high sulphur content. In a particular seam, total-, pyritic- and organic-sulphur contents increase from the floor to the roof of the seam. Upper seams are found to contain, in general, more sulphur than the seams lying below. Certain sections of a seam have low organic sulphur contents which can be mined separately. It is possible to delineate the low sulphur zones in a particular coalfield so assisting the scientific exploration and exploitation.     

Heavy media separation of SRC-II feedstocks: 1. Effect on coal properties

The objectives of this investigation were to determine the effects of coal preparation on the properties of Run-of-Mine (ROM) and washed Powhatan and Ireland Mine coals and to assess the potential effects on SRC-II liquefaction yields. The effect of washing on the two coals was found to be quite similar. For both coals, the properties were altered more significantly by changes in separation media gravity than by changes in the coal size. The elemental composition of the Powhatan and Ireland washed coals was correlated with carbon content. It was shown that both the hydrogen and oxygen levels increased linearly with the carbon content of the coal samples. However, the $\text{H}\text{C}$ and $\text{O}\text{C}$ ratios were not changed significantly by coal cleaning. Only small variations in the nitrogen and organic sulphur levels were observed while the sulphate sulphur and chlorine levels were not affected by coal cleaning. The major impact of the coal cleaning was to reduce the pyritic sulphur (and hence the total sulphur) content of the coals. Most of the pyritic sulphur was shifted into the middling coal and refuse fractions while the clean coals had much lower contents and the pyritic sulphur level decreased with increasing carbon content. Coal cleaning did not significantly alter the maceral contents of vitrinite, exinite, total reactive macerals (TRM), or the reflectance of vitrinite; all these parameters varied over a very narrow range, probably within the precision of the measurement technique.     

Aromaticity of some high sulphur coals: surprising degree of heterogeneity

Aromaticity values for a set of 26 coals of high sulphur content have been determined by a cross-polarization magic-angle-spinning ¹³C n.m.r. Unlike various sets of coals for which similar data are in the literature, this set shows essentially no correlation between aromaticity and carbon content; the variance explained (R²) by a linear regression of the data for the 26 coals is 3%. It appears that this set of coals, all of high vitrinite content and all of Pennsylvanian age, is more heterogeneous than expected, and we infer that the heterogeneity arises at least partly from variation in the distribution of types of structure containing the organic sulphur.     

Statistical analyses and prediction of coking properties of coal

Using regression analyses between the properties of coals and the strengths of their cokes several significant correlations are derived, which are useful to evaluate coals in the making of metallurgical coke. Slight but significant modification was necessary for their application to coal blends. For example, plasticities of the coal blends required a different equation from that derived for the single coals. The region of high coke-strength in the diagram of volatile matter vs. total dilatation was expanded considerably towards coals of lower caking properties by blending of coals, suggesting that the blending may serve to increase the coking properties of component coals. The coke strength, especially after the gasification was found to increase with the increasing inert maceral content in the parent coals up to 30 wt %. The high level of strength was maintained even above 35 wt % of inert content.     

Liquefaction characteristics of selected vitrinite- and liptinite-rich coals from British Columbia,Canada

Four coals from British Columbia, Canada are described micropetrographically, and their liquefaction potential was tested in a rocking autoclave system. Rank was determined by measuring vitrinite reflectances and was found to range from subbituminous C to high volatile A bituminous. Composition was determined by maceral analysis. All four coals were found to be extremely high in the reactive maceral groups vitrinite and liptinite (> 97%) and were thus considered to be susceptible for liquefaction.Results of the liquefaction experiments indicate that in fact all four coals were converted easily into liquid and gaseous products. Overall conversion was found to be >90% and liquid yields (THF solubles) were beyond 80%. Alginite-rich coals from southeastern British Columbia were found to produce greater amounts of gases, indicating that temperatures used in the experiments might have been excessive for liquefaction of alginite-rich coals. Higher liquid yields and less gaseous products were obtained from the vitrinite-rich coals from northeastern British Columbia, indicating that these coals might have the optimum blend of vitrinite/liptinite macerals.     

中国煤中硫的分布特征及成因

通过对全国26个省、市、自治区采集的290个煤样中全硫含量进行分析测试,从不同地质时期、不同变质程度、不同地区以及四大聚煤区等方面,系统分析和考查了中国煤中硫的分布状况.结果表明,我国煤主要以中、低硫煤为主,煤中硫分储量加权平均值为0.94%.高硫煤及特高硫煤来自石炭和二叠纪,其他各时期煤均属于中、低硫煤.随着煤炭变质程度的增高,硫分有增高趋势,主要是由不同的成煤时期沉积环境影响造成.各大聚煤区煤中硫分含量差别很大,自北向南有逐渐增高趋势.     

Semi-quantitative ESCA examination of coal and coal ash surfaces

Four North American coals and their ashes were examined using the direct, surface sensitive technique of X-ray photoelectron spectroscopy (ESCA). Two US National Bureau of Standards reference coals (SRM 1632a, SRM 1635) and one ash (SRM 1633a) were used for instrument calibration. These results verified the semi-quantitative nature of ESCA and its previously determined element detection level of ≈ 10^?9 gm cm^?2 of surface (≈0.1 bulk wt%). Thus, major elements and surface concentrated trace elements were detectable for these samples. ESCA detected elements present in the coal and/or ash in different chemical environments, for example sulphur as the sulphide or sulphate and carbon as graphite, carbonyl, carboxyl or hydrocarbon. The results of this preliminary study indicate that ESCA is useful to elucidate element siting within coal; information that is difficult to determine by analytical techniques requiring sample destruction prior to analysis. Several raw coals contained fluorine and chlorine near the one per cent level. Ashing effectively concentrates the mineral fraction of a coal by an order of magnitude resulting in additional elements being detected by ESCA. The resultant detection level of elements in the original coal is thus lowered to ≈0.01 bulk wt% by ashing. It was found that fluorine and sulphur were highly concentrated on several coal ash surfaces possible indicating surface Sorption reactions during combustion. Application of ESCA in coal geochemistry and mineralogy is indicated by this study. ESCA has the potential to measure elements at the minor and possibly trace level and confirm element siting within coal and coal ash. In addition, it may be possible to identify coals from different deposits by their unique broad scan ESCA spectra fingerprints.     

Supercritical gas extraction of Victorian brown coals: The effect of coal properties

A selection of fifteen Victorian brown coals, which varied in lithotype but only slightly in rank, were subjected to supercritical gas extraction with toluene. Seven of these coals were also extracted with 5% tetralin/toluene under the same conditions of temperature and pressure (400 °C and 10 MPa). The overall conversion, the extract yield and the yield of toluene solubles (oil and asphaltene) were correlated with more easily obtained coal properties using simple linear regression analysis. Good correlations were obtained between the total conversions and the volatile matter content of the coals, and for the toluene extractions between both the extract yield and the yield of toluene solubles and the H/C atomic ratio. For the toluene solubles from the toluene extractions, the aromaticity decreased and the molecular weight increased as the H/C atomic ratio of the coal increased. Inorganic constituents of the coals did not appear to have a marked effect on total conversion and liquid yields. Removal of the cations from two coals increased conversion and liquid yields in one case and decreased these in the other, but in both instances the changes were not large.     

Ash deposition characteristics of Moolarben coal and its blends during coal combustion

We report a systematic and comprehensive laboratory investigation of the ash deposition behavior of Moolarben (MO) coal, which has recently begun to be imported into Korea. Ash deposition experiments were conducted in a drop tube reactor, and a water-cooled ash deposit probe was inserted into the reactor to affix the ash. The tests were conducted using five types of single coals (two bituminous and three sub-bituminous, including MO coal) and blended coals (bituminous coal blended with sub-bituminous coal). Two indices represent ash deposition behavior: capture efficiency and energy-based growth rate. A thermomechanical analysis evaluated the melting behavior of the resulting ash deposits. The MO coal had the least ash deposition of the single coals due to its high melting temperature, indicated by high ash silica content. Indonesian sub-bituminous coals formed larger ash deposits and were sticky at low temperatures due to relatively high alkali content. However, blends with MO coal had greater ash deposition than blends with other bituminous coals. This non-additive behavior of MO coal blends is likely due to interactions between ash particles. Coals with higher silica content more effectively retain alkali species, resulting in lower melting temperatures and larger ash deposits. Therefore, we recommend that when blending in a boiler, silica-rich coals (SiO₂>80%, SiO₂/Al₂O₃> 5) should be blended with relatively low-alkali coals (Na₂O+K₂O<3%), and the blending ratio of the silica-rich coals indicates less than 10%, which can safely operate the boiler.